Various kinds of implantable medical leads for providing stimulation to selected body tissue have become available. For example, an implantable cardiac lead delivers electrical therapy to a patient's heart through one or more electrodes on the distal end of the lead. The electrodes are connected via electrical conductors to a connector assembly on the proximal end of the lead. The connector assembly is in turn coupled to an implantable medical device (IMD) such as a pacemaker or an implantable cardioverter-defibrillator (ICD) or to an IMD combining both pacemaker and ICD functions.
The electrical conductors of an implantable lead are enclosed within an elongated, typically tubular housing made of an insulating material such as silicone rubber or polyurethane. Silicone rubber is known to have superior flexibility and long term biostability but has relatively poor abrasion and tear resistance. Polyurethane, on the other hand, is more resistant to abrasion, cuts and tears but is susceptible to biodegradation and is somewhat stiffer than silicone rubber.
It is desirable that the outer surface of an implantable medical lead have resistance to abrasive wear in the event the lead body rubs against another lead, another implanted device, or the patient's anatomical structure while in use after implantation. Abrasive wear can eventually cause breaks or tears in the lead body's insulating housing and consequent failure of the electrical connection provided by one or more of the electrical conductors. A short circuit, in particular, can potentially damage the circuits of the IMD to an extent requiring its replacement. Insulation abrasion failures account for the largest proportion of all failures in silicone rubber insulated leads.
Thus, there continues to be a need for implantable medical leads, and particularly those with silicone rubber housings, having improved abrasion and tear resistant properties.